Using the ROLLUP Clause

The ROLLUP clause extends GROUP BY to return a row containing a subtotal for each group along with a total for all groups. As you saw in Chapter 3, you use GROUP BY to group rows into blocks with a common column value. For example, the following query uses GROUP BY to group the rows from the employees2 table by department_id and uses SUM() to get the sum of the salaries for each division_id:

SELECT division_id, SUM(salary)
FROM employees2
GROUP BY division_id;

DIV SUM(SALARY)
--- -----------
BUS     1610000
OPE     1320000
SAL     4936000
SUP     1015000